Multi cell cooperation has been proposed to increase performance and communication capacity of wireless communication systems. The multi cell cooperation is also called CoMP (cooperative multiple point transmission and reception). The CoMP is called MIMO (Multiple Input Multiple Output) in a meaning that transmitting antennas are like a multiple antenna system distributed in a plurality of cells, because the antennas disposed of each base station does not independently operate, but operate in consideration of users in other cells.
In the CoMP, there are a beam avoidance technique that mitigates interference with a user at the cell interface by cooperation of adjacent cells and a joint transmission technique that transmits the same data by cooperation of adjacent cells.
In particular, in the next wireless communication systems, such as IEEE (Institute of Electrical and Electronics Engineers) 802.16m or 3GPP (3rd Generation Partnership Project) LTE (long term evolution)-Advanced, it has been an important requirement to improve performance of users who are positioned at a cell interface and significantly interfered with adjacent cells. The beam avoidance technique has been considered to remove this problem.
The beam avoidance technique mitigates interference from cooperative cells by sharing channel information between the cooperative cells. In general, the beam avoidance controls the interference by limiting PMI (Precoding Matrix Indicator) that cooperative cells can select.
According to R1-091252, “Estimation of extended PMI feedback signaling required for user intra-cell and inter-cell coordination”, disclosed in April, 2009, a user determines the PMI and CQI (Channel Quality Indicator) of a serving cell, and then the PMI of a cooperative cell having the smallest interference and the increase of the CQI when the cooperative cell finally uses the PMI is fed-back to the cooperative cell. On the contrary, a method of feed-backing the PMI of a cooperative cell having the largest interference and the increase of the CQI when the cooperative cell does not finally uses the PMI to the cooperative cell.
It is required to share various information between a serving cell and cooperative cells to achieve the CoMP. Various feedback information between a user equipment and a serving cell and/or a user equipment and a cooperative cell is needed to share information.
However, signaling overhead may be caused, when large amount feedback information is used for the CoMP.
A multi cell cooperation technique that can reduce feedback overhead while mitigating interference is required.